This paper summarizes a multi-year research program to address the decanting of water from oil spill fluids recovered by skimmers. The first series of tests, with two weir-type skimmers at Ohmsett, was conducted to study the rate and amount of free water separation that can be expected in temporary storage containers. The goal of this study was to predict the best time to decant water back into the boomed area and optimize the available onsite storage space. The results indicated that “primary break” (the initial separation of the recovered liquids) occurred within a few minutes to one hour, depending on the physical characteristics of the oil. Rapidly decanting this free water layer may offer immediate increases of 200 to 300% in available temporary storage volume. Initial oil concentrations in the decanted water also depended on the physical properties of the oil; they ranged from 100 to 3000 mg/L These declined by a factor of approximately 3 after one hour of settling, and by a factor of approximately 5 after one day. The second series of tests was undertaken to develop a more complete understanding of the use of emulsion breakers injected into an oil spill recovery system at both lab-scale (at SL Ross) and mid-scale (at Ohmsett). The experiments were designed to assess the injection/mixing/settling regimes required for optimum water-removal from a meso-stable water-in-oil emulsion with an oil spill demulsifier. The use of a demulsifier injected into a recovery system, combined with decanting, did substantially reduce the volume of water in temporary storage tanks and the water content of emulsions for disposal/recycling.

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Author notes

1 This paper has been reviewed by the U.S. Minerals Management Service staff for technical adequacy. The opinions, conclusions, and recommendations contained in this paper are those of the authors and do not necessarily reflect the views and policies of the U.S. Minerals Management Service. The mention of a trade name or any commercial product in this report does not constitute an endorsement or recommendation for use by the U.S. Minerals Management Service. Some of the research described in this report was also supported by the Alaska Department of Environmental Conservation. The findings and conclusions presented by the authors are their own and do not necessarily reflect the views or position of the Department.